The present invention relates to an apparatus for removing a sample of at least one phase from a moving mixed phase consisting of two liquids which have different densities and which are substantially mutually insoluble, and which form a dispersed phase and a continuous phase.
In many chemical processes operating with liquids, particularly in liquid-liquid countercurrent extraction processes, it is necessary, for reasons of process control or control of the desired operating states, to take samples. In such a process, two liquids which are insoluble or hardly soluble in one another may be moved or transported in a pipe or column. If these liquids are mixed for process reasons, the taking of a sample has in the past been effected, for example, by extracting the mixed phase from the pipe or column by means of a sampling tube or sample taking system as provided by Professor Hartland, ETH, Zurich. If the mixing of the liquids is effected for reasons of transferring substances from one liquid to the other, transfers of the substance cannot be prevented from taking place during the time when the mixed phase has been extracted from the column, but separation of the two liquid phases has not yet taken place. During the subsequent analytical examination of the substance concentrations in the liquids, errors up to 100% may then occur.
The sample taking system according to Professor Hartland, which essentially comprises a metal cylinder with a Teflon cap containing a perforated screen, makes it possible only to extract the lighter phase from the moving mixed phase. The extraction rate, however, must be kept low, at less than 1 ml per minute, since at higher rates the heavier phase would be extracted as well. This is particularly unsuitable if the light phase is the dispersed phase and the heavy phase is the continuous phase.
Another disadvantage of the prior art devices is the possibility of clogging of the fine bores at the sample taker input and in the soiling or covering of the surface of the material of the sample taker, which is specific for each phase, after long periods of operation. This results in a reduction of separation of the extracted liquid. A further disadvantage, in the case of a pulsating liquid-liquid countercurrent extraction column, is the effect of the pulsation on the hydraulic conditions in the sample taker. Moreover, the relatively complicated structure of the sample taking system according to Professor Hartland and the difficult cleaning connected therewith, which is done, for instance, with compressed air for which efficiency is not always assured, is a further disadvantage.